Abstract: Aiming at the three-phase voltage unbalance problem of the interconnected power supply system of traction substation groups, a negative sequence centralized compensation scheme and control strategy based on three-phase transformer and static var generator（SVG） are proposed. First, according to the power transformation relation of the traction transformer and different load conditions, general power compensation expressions of compensation devices for the traction load in two modes are deduced.According to the power quality standards in China, a double-limit compensation scheme is proposed aiming at satisfactory negative sequence compensation, which includes mode selection method, SVG capacity configuration method and SVG operation method.According to the compensation scheme, the SVG double closed-loop compensation control strategy with mode discrimination is designed. Then, the compensation scheme is validated with measured data of traction substations, which proves that the scheme has good compensation effect. Compared with the complete compensation scheme, the proposed scheme requires smaller device capacity. Finally, it is proven through simulations that the control strategy is effective in negative sequence compensation and has fast response speed.